High-level and low-level are terms used in classifying levels of description and goals in many fields where systems could be described from different perspectives.
A high-level description is one that is more abstracted, describes overall goals and systemic features, and is typically more concerned with the system as a whole, or larger components of it.
A low-level description is one that describes individual components, provides detail rather than overview, rudimentary functions rather than complex overall ones, and is typically more concerned with individual components within the system and how they operate.
Low and high level are relative; for example the graphics engine that drives a computer game and works at the level of entities in the game, is high level compared to the video subsystem DirectX that works on the level of renderable objects, which itself is high level compared to a vertex shader within that system.
Due to the nature of complex systems, the high-level description will often be completely different from the low level one. For example, there are features to an ant colony that are not features of any individual ant; features of the human mind that are not known to be descriptive of individual neurons in the brain, features of oceans which are not features of any individual water molecule, and features to a human personality that are not features of any cell in a body. The descriptions of these differ depending at what level they are studied. Features which emerge only at a high level of description are known as epiphenomena.
The instruction "write a creative poem on love" is a high-level instruction. The instruction "tighten the tendons in the dominantwrist to grip the pen" is a low-level description of an activity within that.
"Wikipedia is an encyclopedia" is a high-level description compared to "Wikipedia is a collection of textual articles on many topics". The former reflects a higher level view of organization, purpose, concept and structure, but does not explain what Wikipedia physically is. The latter is more detailed as to what exactly Wikipedia contains and how it's made up, but doesn't explain what its overall purpose and goals are. These are typical features of high-level and low-level descriptions.